1. Field of the Invention
The present invention relates to an apparatus and method using wireless communication, such as a wireless LAN (Local Area Network), and a signal attenuation prediction apparatus and method.
2. Description of the Related Art
In recent years, battery-driven terminals having wireless communication capabilities have been widely used. An example of the wireless communication capability may be a wireless LAN (Local Area Network), such as IEEE 802.11a/b/g.
In related art, a major challenge of a desktop wireless communication instrument that uses transmitting and receiving terminals having a fixed distance therebetween is maximization of communication speed and improvement of stability, while a challenge of a battery-driven mobile terminal is increase in continuous operating time without recharging as well as maximization of communication speed and improvement of stability. That is, in a battery-driven wireless LAN device, reduction in power consumption is a major challenge to address.
As one effective method for reducing power consumption, attention is given to a control method for optimizing transmission power according to the transmission channel characteristic. Intuitively speaking, it is easily conceivable that transmitting and receiving terminals communicate with each other using relatively low transmission power when they are within a short distance, while these terminals use higher transmission power as the distance between them increases, so as to reduce unnecessary transmission power. That is, when data is sent, transmission power is controlled such that power consumption is minimized on the transmitter side to the extent that the receiver may always normally receive packets, thereby allowing reduced unnecessary power consumption.
JP-A-7-143047 describes a wireless relay apparatus that, whenever the receiver receives a signal, feeds the level of the signal back to the transmitting side so as to update the transmission signal level to an appropriate value. JP-A-2005-117303 describes a method for determining optimum transmission power in wireless LAN communication when reception power intensity and PER (Packet Error Rate) is obtained.
Focusing on IEEE 802.11h, it defines TPC (Transmit Power Control) as measures to minimize radio interference into neighboring areas and describes the possibility of reducing power consumption of a TPC-implemented transmission terminal. Particularly, “Energy-Efficient PCF Operation of IEEE 802.11a Wireless LAN”, Qiao, etc, IEEE INFOCOM 2002 (hereinafter referred to as “Qiao”), which was used as a reference material in the standardization drafting work, analyzes in detail the power saving effect in a TPC-operated mobile terminal. “Qiao” describes that an equation for evaluating power consumption per transmission bit is derived using two variables of the modulation method and transmission power, and significant power consumption reduction can be achieved when an optimum modulation method and transmission power are given from the evaluation equation.